Traditionally, high pressure hoses have been made using the same materials for the inner tube and the outer cover. In other words elastomer or rubber hoses have been constructed using a rubber inner tube and a rubber cover. So called thermoplastic or plastic hoses have been constructed using a thermoplastic inner tube and a thermoplastic cover.
For purposes of the present invention described herein, it is important to provide the definitions of “rubber” and “plastic”. As used herein the term “rubber” is synonymous with “elastomer” and refers to thermosetting, crosslinking, or curable materials, including natural and synthetic rubbers such as, but not limited to Neoprene®, nitrile, Buna N, styrenebutadiene rubber (SBR), Hypalon™, silicone and the like. Modern elastomeric materials are often devised of more than one rubber material and may contain other additives and/or be comprised of additional elements such as one or more thermoplastic constituent(s).
Elastomeric materials require a process of curing or vulcanization. Various methods of curing have evolved over the years and for the purposes of this invention, conventional methods known to those familiar with the art apply. One common method is curing in a steam autoclave. Elastomeric materials are also considered to be thermosetting, a term that means once cured, they will not return to a liquid state.
As used herein, the term “thermoplastic” means materials which are solid at room temperature and which soften at an elevated temperature repeatedly. Some examples, but by no means all that may apply to this invention, include thermoplastic materials such as nylon, polyester terephthalate, polyethylene, polyvinyl chloride, polyamide (nylon), ethylene vinyl acetate, polypropylene and polyurethane. Modern thermoplastic materials are often devised of more than one thermoplastic material and may contain other additives and/or be comprised of additional elements such as one or more elastomeric or rubber constituent(s).
As stated previously, modern polymers, whether thermoplastic or elastomeric, often contain constituents of the other. Thus, a material is considered elastomeric if it requires curing although it may contain a constituent or constituents of thermoplastic and/or other additives. Conversely, a thermoplastic material is still considered thermoplastic if it can achieve a liquid state at a certain high temperature, even if it includes a constituent or constituents of rubber and/or other additives. For purposes of the present invention, materials are considered thermoplastic or elastomeric if they retain the processing properties as defined herein, even if they contain components or constituents of the other.
Wire and textile reinforced elastomeric and thermoplastic hoses are ubiquitous. So much so that the Society of Automotive Engineers (SAE) has adopted detailed standards that describe the materials used in their construction, dimensional tolerances and the dynamic test parameters for a wide range of hoses. Such details are amply described in the standards SAE J343 (2004-01) and SAE J517 (2008-11). Virtually all high pressure hoses in use today are consistent with performance criteria and materials as described in SAE J517 and SAE J343 at least on a conceptual basis. Design differentiation is employed when a particular niche application places different demands on the hose. Such demands may require a higher technical level of performance or a lower level of performance. In addition to the definitive U.S. standards of SAE J343 and SAE J517, there are international standards, including (ISO) International Standards Organization, DIN (Deutsche Industrial Norms), BS (British Standards), EN (European Norm), and the like. All standards are basically similar and often cross reference one another. The methods of manufacturing the all-rubber and all-thermoplastic hoses are well known to those familiar with the art. Within the SAE J517 and SAE J343 documents there are described three main types of high pressure hydraulic hose: steel wire braided rubber; steel wire spiralized rubber and; yarn braided thermoplastic.
U.S. Pat. No. 3,725,167 and U.S. Pat. No. 4,604,155 teach various methods of making steel wire braided rubber high pressure hose Such hoses exhibit excellent flexibility, fitting retention, kink resistance and impulse life but are known not to be as good in terms of abrasion as hoses with engineered thermoplastic cover sheaths.
U.S. Pat. No. 4,175,992 teaches various methods of making steel wire spiralized rubber high pressure hose. Such hoses exhibit excellent very high pressure performance, fitting retention, kink resistance and impulse capabilities, but because they have as many as six layers of reinforcement are generally very stiff particularly on the larger sizes.
U.S. Pat. Nos. 3,251,381 and 3,116,760 teach various methods of making yarn reinforced thermoplastic high pressure hoses. Such hoses exhibit excellent high pressure performance, impulse life, and abrasion resistance, but are known to be prone to kinking and poor fitting retention problems at high temperatures particularly if the increase in temperature approaches the melt temperature of the material used in inner tube and cover sheath.
There exists a need to incorporate the best individual features of the three basic types of hose and therefore, in recent years, various efforts have been introduced to “hybridize” or impart features or methods that cross over from one or more of the three concepts described previously. Such attempts have only been marginally successful in niche applications and have often required one benefit to be sacrificed to gain another.
U.S. Pat. No. 4,341,578 teaches methods to use braided wire instead of yarn in the manufacture of thermoplastic hose. The result is improvement in fitting retention, but the hose itself remains very stiff. Such stiffness makes the hose acceptable for a permanent installation, but for practical purposes cannot be used as a spray hose.
In an effort to improve the known abrasion deficiencies of known rubber covered hoses, U.S. Pat. No. 5,145,628 teaches a method whereby an ultra high molecular weight polyethylene (UHMWPE) is applied by wrapping a tape of same over an extruded sheath covering wire braided or spiralized rubber hose. UHMWPE is known to be very expensive even though it has superior abrasion resistance, which in some applications is desirable. While UHMWPE is a thermoplastic material, the process requires the thermoplastic cover sheath to be applied over an extruded rubber sheath and then vulcanized.
U.S. Pat. No. 5,964,409 teaches a yarn reinforced thermoplastic hose for high pressure spraying whereby the inner tube and cover are produced with highly plasticized thermoplastic materials free of a rubber constituent. The result is an inexpensive hose, but the impulse life and temperature resistance are dramatically below those described in SAE J343 and SAE J517. The hose shows some improvement in flexibility, but is still relatively stiff, prone to kinking, has a low temperature rating and is generally poor in terms of fitting retention. Such a hose is acceptable for light duty spray applications, but would not be acceptable for hydraulic applications because of limits in temperature and impulse life which are well below those noted in SAE J343 and SAE J517.
U.S. Pat. No. 7,222,644 teaches a steel wire reinforced thermoplastic hose for high pressure spraying whereby the inner tube and cover are produced with highly plasticized thermoplastic materials. The result is a hose that is still very stiff although fitting retention is better than a textile yarn reinforced version. Again, such a hose may be acceptable for light duty spray applications, but would not be acceptable for hydraulic applications because of limits in temperature and impulse life which are well below those noted in SAE J343 and SAE J517.
It is generally known to those familiar with the art that wire braided high pressure rubber hoses are substantially more flexible and less prone to kinking than their thermoplastic counterparts with the same performance specifications as described within SAE J343 and SAE J517. For example, the performance specifications for SAE100R18 yarn reinforced thermoplastic hose are exactly the same as for SAE100R17 wire braided rubber hose. Yet, the rubber hose is nearly impossible to kink and remains highly flexible. U.S. Pat. No. 7,222,644 describes thermoplastic hoses with a bend radius as small as 30 mm. An equivalent wire braided all rubber hose will not kink, for example, in a nominal ¼″, 5/16″ and ⅜″ (nominal inside diameter dimensions defined by SAE) size even below 30 mm if the method for measuring the bend radius described in this '644 patent is used.
On the other hand, thermoplastic hoses are known to be far superior in terms of abrasion, ozone and ultraviolet light resistance by comparison to natural and synthetic rubber compounds. An ideal hose would exhibit the known flexibility of a reinforced rubber hose, combined with a highly flexible, resilient thermoplastic cover.
There is therefore a need for an improved high pressure hose that meets the requirements of all relevant standards while combining the most desirable qualities of both all-elastomeric and all-thermoplastic hoses and which can be produced at a reasonable cost.